It is well established that nutritional status plays an important role in the onset of puberty. It has been proposed that changes in the metabolic state of the maturing animal may directly influence neuroendocrine factors associated with the timing of puberty. We propose that diet, in particular, a high fat diet, through metabolic and endocrine changes may directly influence sexual maturation and the timing of first ovulation, independent of changes in overall growth. We will examine the effect of different diets (high fat-high protein, high fat-low protein, high carbohydrate-high protein and standard high protein chow) on growth and sexual maturation and the timing of first ovulation using the prepubertal rhesus female, housed outdoors, as a model. Starting at 12 mo of age, we will examine the effects of diet on: (a) somatic growth, reflected in body weight, crown-rump lengths, percent body fat and adipose cellularity; (b) growth related endocrine factors including growth hormone (GH), somadomedin-C (SM-C), prolactin, glucose, and insulin; (c) food intake and energy expenditure, reflected in basal metabolic rate, and (d) possible seasonal patterns in growth, feeding and energy expenditure. The effect of these regulatory changes in relation to sexual maturation will be examined by monitoring maturational increases in gonadal steroids and gonadotropin secretion. Developmental and diet-induced changes in gonadal status in relation to changes in the metabolic and reproductive state (insulin, GH, SM-C, LH) will be examined by measuring ovarian steroid concentrations and the major pathways for estradiol metabolism. Finally, we will examine more closely effects of diet on metabolic factors (insulin, free fatty acids, glucagon, large neutral amino acids) by measuring concentrations before and after administration of a glucose load (iv glucose tolerance test). This project will provide new information on the effects of diet and metabolism on sexual maturation and the timing of first ovulation.